Infrastructure equipment, mobile communications network and method for reducing overhead of signaling transmissions and processing

ABSTRACT

A communications device establishes a communications context for communicating data packets using a packet communications bearer from the communications device via a mobile communications network. A controller of the communications device is configured to identify that the communications device can enter a stasis state because no data packets are available for transmission for a predetermined time via the packet communications bearer or there are no data packets to receive via the packet communications bearer, to transmit a stasis state message to the mobile communications network, and to store information relating to the communications context associated with the packet communications bearer in a data store. The stored information can be used by the controller to re-establish the packet communications bearer to transmit and/or receive data packets using the packet communications bearer, the communications device thereby entering the stasis state.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of and claims the benefit ofpriority under 35 U.S.C. § 120 from U.S. application Ser. No.14/781,750, filed Oct. 1, 2015, which is based on PCT filingPCT/GB2014/050973 filed Mar. 27, 2014, and claims priority to BritishPatent Application 1307188.1, filed in the UK IPO on Apr. 22, 2013, theentire contents of each of which is being incorporated herein byreference.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates to infrastructure equipment for mobilecommunications networks, mobile communications networks and systems andmethods of communicating using mobile communications networks.

BACKGROUND OF THE DISCLOSURE

Mobile communications systems continue to be developed to providewireless communications services to a greater variety of electronicdevices. In more recent years, third and fourth generation mobiletelecommunication systems, such as those based on the 3GPP defined UMTSand Long Term Evolution (LTE) architectures have been developed tosupport more sophisticated communications services to personal computingand communications devices than simple voice and messaging servicesoffered by previous generations of mobile telecommunication systems. Forexample, with the improved radio interface and enhanced data ratesprovided by LTE systems, a user may enjoy high data rate applicationssuch as mobile video streaming and mobile video conferencing that wouldpreviously only have been available via a fixed line data connection.The demand to deploy third and fourth generation networks is thereforestrong and the coverage area of these networks, i.e. geographiclocations where access to the networks is possible, is expected toincrease rapidly.

More recently it has been recognised that rather than providing highdata rate communications services to certain types of electronicsdevices, it is also desirable to provide communications services toelectronics devices that are simpler and less sophisticated. Forexample, so-called machine type communication (MTC) applications may besemi-autonomous or autonomous wireless communication devices which maycommunicate small amounts of data on a relatively infrequent basis. Someexamples include so-called smart meters which, for example, are locatedin a customer's house and periodically transmit information back to acentral MTC server data relating to the customer's consumption of autility such as gas, water, electricity and so on.

Whilst it can be convenient for a communications device such as an MTCtype device to take advantage of the wide coverage area provided by athird or fourth generation mobile telecommunication network there are atpresent disadvantages. Unlike a conventional third or fourth generationcommunications device such as a smartphone, a lower complexity devicemay operate with a lower bandwidth and be preferably relatively simpleand inexpensive. The type of functions performed by the MTC-type device(e.g. collecting and reporting back data) do not require particularlycomplex processing to perform.

As will be appreciated, there may be a desire for many types ofcommunications devices and mobile communications networks to usecommunications resources as efficiently as possible and to reduce powerconsumption. It is known for example to reduce the power consumed by acommunications device by performing what is known as discontinuousreception. Discontinuous reception is a technique in which acommunications device may be radio resource connected, but aftermonitoring a control channel to determine whether communicationsresources have been allocated to the communications device, thecommunications device can sleep for a remainder of a time before anothertransmission may occur on the control channel. A communications devicemay also be configured with a short and a long discontinuous receptiontimer. If no activity is detected for a short discontinuous receptiontime, then the communications device moves to a long discontinuousreception timer. Accordingly the communications device can save power.

SUMMARY OF THE DISCLOSURE

Embodiments of the present disclosure can provide in one example acommunication device for transmitting data to and receiving data from amobile communications network. The mobile communications networkincludes one or more network elements providing a wireless accessinterface for communicating with the communications device. Thecommunications device comprising a transmitter unit configured totransmit signals to the mobile communications network via the wirelessaccess interface provided by the one or more network elements of themobile communications network, and a receiver unit configured to receivesignals from the mobile communications network via the wireless accessinterface provided by the one or more network elements of the mobilecommunications network, and a controller. The controller is configuredto control the transmitter unit to transmit one or more signallingmessages to the communications network and the receiver unit to receiveone or more signalling messages from the communications network toestablish a communications context for communicating data packets usinga packet communications bearer from the communications device via themobile communications network. The controller is configured to identifythat the communications device can enter a stasis state because no datapackets are available for transmission for a predetermined time via thepacket communications bearer or there are no data packets to receive viathe packet communications bearer, to transmit a stasis state message tothe mobile communications network, and to store information relating tothe communications context associated with the packet communicationsbearer in a data store. The stored information can be used by thecontroller using the transmitter unit and the receiver unit tore-establish the packet communications bearer to transmit and/or receivedata packets using the packet communications bearer, the communicationsdevice thereby entering the stasis state.

Embodiments of the present technique can provide can arrangement inwhich a communications device can enter a stasis state in which acurrent state of protocols associated with a communications bearer forboth the wireless access interface and via a mobile communicationsnetwork are saved. However radio resources associated with thecommunications context and therefore the communications bearer arereleased for allocation to other communications devices. If the mobilecommunications device then needs to transmit or receive data for exampleif there are data packets to be transmitted via the mobilecommunications network, then the communications device can transmit arequest message to transit from the stasis state to the connected state,re-establishing the communications bearer by recovering from the datastore the state of the protocols of the communications bearer as definedby the communication contexts as they were saved before the stasisstate. Accordingly there is a saving in both communications resourcesand power because the previous communications context and communicationsbearer has been saved and therefore does not need to be established. Incontrast conventional techniques would require that the radio resourcesand the communications bearer are released by the mobile communicationsnetwork so that the communications device would have to re-create acommunications context by performing a routine which requires anexchange of messages with the mobile communications network. Accordinglythere is a saving in both communications resources and power consumed bythe communications device.

In a radio resource idle state, a communications device isconventionally arranged to respond to a paging message transmitted bythe communications network. The occasions when it may be paged, areindicated by System Information and these must coincide with theOnDurationTime of RRC_CONNECTED discontinuous reception so that thecommunications monitors control channels such as the PDCCHs in order todetect a paging identifies such as a P-RNTI. As such, in some examplesthe communications device may be configured to move out from the stasisstate into the connected state in order to receive downlink data packetsafter receiving a paging message.

Further aspects and features of the present disclosure are defined inthe appended claims, including but not limited to, a mobilecommunications device, a method of communicating, a networkinfrastructure element, a communications network and the method ofcommunicating via a wireless access interface.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present disclosure will now be described by way ofexample only with reference to the accompanying drawings in which likeparts are provided with corresponding reference numerals and in which:

FIG. 1 provides a schematic diagram illustrating an example of a mobilecommunications network configured in accordance with LTE:

FIG. 2 provides a schematic diagram illustrating an arrangement of anEnhanced Packet Service bearer established for communicating datapackets via the mobile communications network;

FIG. 3 provides a schematic diagram representing the states of thecommunications device including whether the device is EMM registered orECM connected;

FIG. 4 is a schematic illustration of state transitions of acommunications device operating in the mobile communications network ofFIG. 1;

FIG. 5 is a simplified call flow diagram illustrating a process in whicha communications device establishes and an EPS bearer for communicatingdata via the mobile communications network shown in FIG. 1;

FIG. 6 is a schematic block diagram illustrating functions performed byinfrastructure equipment of the mobile indications network shown in FIG.1 to provide an EPS bearer;

FIG. 7 is a schematic block diagram illustrating the protocol stack fora control plane of infrastructure equipment forming part of the mobilecommunications network shown in FIG. 1;

FIG. 8 is a schematic block diagram illustrating the protocol stack foruser plane of a communications device (UE) and is a base station (eNB);

FIG. 9a is a call flow diagram illustrating an exchange of signallingmessages between a communications device and infrastructure equipment ofthe mobile communications network shown in FIG. 1 to establish acommunications context; and FIG. 9b is a corresponding call flow diagramillustrating an exchange of messages to release communicationsresources;

FIG. 10 is a schematic illustration of a state diagram of acommunications device operating in accordance with the present techniquewhich includes a new stasis state;

FIG. 11 is a schematic illustration of state transition diagram of acommunications device which transitions to a stasis state in accordancewith the present technique;

FIG. 12 is a call flow diagram illustrating an exchange of messageswhich includes the operation of a communications device which enters astasis state in accordance with the present technique; and

FIG. 13 provides a schematic block diagram of a communications deviceand a base station configured in accordance with an example of thepresent disclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS

The example embodiments will be generally described in the context of a3GPP LTE architecture. However, the invention is not limited to animplementation in a 3GPP LTE architecture. Conversely, any suitablemobile architecture is considered to be relevant.

Conventional Network

FIG. 1 provides a schematic diagram illustrating the basic functionalityof a conventional mobile telecommunications network. The networkincludes one or more base stations 102 (one base station represented)connected to a serving gateway (S-GW) 103 for traffic in the user planeand to a Mobility Management Entity (MME) for signalling in the controlplane. In LTE, the base stations are called e-NodeB, which are referredto in the following description as eNB. Each base station provides acoverage area 103 within which data can be communicated to and fromcommunications devices 101. Data is transmitted from a base station 102to a communications device 101 within a coverage area via a radiodownlink. Data is transmitted from a communications device 101 to a basestation 102 via a radio uplink. The core network, comprising the MME105, the S-GW 103 and the PDN-Gateway (P-GW) 104, routes data to andfrom the communications devices 101 and provides functions such asauthentication, mobility management, charging and so on. The P-GW isconnected to one or more other networks, which may for example includethe internet, an IMS core network, etc. In the illustration of FIG. 1,connections on the user plane have been represented with a plain linewhile connections on the control plane have been represented with adashed line.

The term communications devices will be used to refer to acommunications terminal or apparatus which can transmit or receive datavia the mobile communications system. Other terms may also be used forcommunications devices such as personal computing apparatus, remoteterminal, transceiver device or user equipment (UE) which may or may notbe mobile.

FIG. 2 illustrates an example of a path followed by a message 130communicated by a communications device 101. In that example an MTCcommunications device 101, wishes to send the message 130 to adestination 120, the destination being reachable via the internet. Inthis example, a destination device is represented as a computer. Howeverthe destination 120 could be an element of any suitable type where theelement can be addressed by the communications device 101. For example,the destination device 120 may be another communications device, apersonal computer, a server, a proxy, or an intermediary element (to afinal destination).

The following description provides a summary explanation of an exampleof operation in which a communications device communicates the message130 via an LTE network, which is helpful in appreciating some aspectsand advantages of the present technique.

In order for the communications device 101 to send data to adestination, an EPS bearer between the communications device 101 and thePGW 104 is set up, the EPS bearer being partially carried over a GTPtunnel between the eNB 102 and the SGW and another GTP tunnel betweenSGW and PGW 104, as illustrated in FIG. 2. As the message 130 is carriedto the destination device, it is sent from the communications device101, at a first end of an EPS bearer to the eNB 102 (step 1), then tothe S-GW 103 (step 2) and then to the P-GW 104 (step 3), at the otherend of the EPS bearer. The P-GW 104 then forwards the message 130 to thedestination 120 (step 4).

FIG. 3 illustrates the various transitions between the four possiblecombinations of ECM states (connected or idle) and EMM states(registered or unregistered) as defined in the LTE standards for acommunications device with a view to illustrating how communicationsdevices' connections are managed. The acronym ECM stands for “EPSConnection Management” and the ECM state generally indicates whether thecommunications device has a Non-Access Stratum (NAS) connection set upwith the MME. In LTE, as the communications device connects to the MMEand switches to ECM_connected, it also sets up an EPS bearer, that is, adata connection to the P-GW via the S-GW. Also, as the communicationsdevice switches from ECM_connected to ECM_idle, the EPS bearer is torndown, and all S1 and RRC connections are released. The acronym EMMstands for “EPS Mobility Management” and the EMM state generallyindicates whether a communications device is attached to the network.When the communications device is in EMM_unregistered, it may forexample be turned off, out of coverage or connected to a differentnetwork. In contrast, when a communications device is in EMM_registered,it is attached to the network and, as such, it has an IP address and aNAS security context in the MME. It may or may not have an EPS bearerset up, but in any case, it has some context associated with it in theMME (e.g. NAS security context) and in the P-GW (e.g. the IP address).In addition the MME will know in which tracking areas the UE is located.The four ECM/EMM states and the transitions between them is describednext.

The communications device 101 is assumed to start from a state 153 inwhich the communications device 101 is not connected to the network. Inthe state 153, the communications device is in EMM_unregistered andECM_idle states. From this state, the communications device can attachto the network to be in EMM_registered and ECM_connected states.However, in order to attach, the communications device cannot switch toEMM_registered if it has not switched to ECM_connected first. In otherwords, starting from state 153, the communications device cannot go tostates 152 or 151 and it has to go to state 154 first. Therefore, asillustrated by arrow 161, a communications device in state 153 canattach to the network by first switching to ECM connected and then toEMM_registered. As a communications device starts an attachmentprocedure from state 153, the communications device moves from a state153 where it does not have any connection to a state 151 where it has aNAS connection to the MME, an IP address allocated by the P-GW, and aEPS bearer to the P-GW via the e-NB and the S-GW.

Transitions between states 151 and 152 occur when a data connection (EPSbearer) is set up (164) or when all data connections have been released(165). Generally, transition 165 occurs when the user had an EPS beareractive and has not been using the bearer for a certain time. The networkcan then decide that the communications device no longer needs an EPSbearer and thus release all the corresponding resources and switch thecommunications device to ECM_idle. Transition 164 generally occurs whenthe communications device has not been using any EPS bearer (see forexample the discussion on transition 164) and now has data to send orreceive. An EPS bearer is then set up for this communications device andit is switched to ECM_connected. Whenever the communications device isEMM_registered, regardless of the ECM states, the communications devicewill have an IP address that can be used to reach the communicationsdevice, in other words an IP context remains active even if no actualEPS bearer is currently active (e.g. state 152).

If the communications device detaches from the network, for examplebecause it is turned off, moving to a different network, or for anyother reason, it will switch from any state it is into state 153,releasing any outstanding EPS bearer or context that was previouslymaintained for the communications device, via transitions 162 or 163.

As can be understood, the state 154 where the communications device isin ECM_connected and in EMM_unregistered is a transient state and thecommunications device does not generally remain in that particularstate. A communications device in that state is either a communicationsdevice switching from state 153 (detached and inactive) to state 151(attached and active) or a communications device switching from state151 to state 153.

RRC states are also provided to reflect the status of the RRC connectionbetween the communications device and the eNB (RRC_connected andRRC_idle). Under conventional operation conditions, the RRC statescorrespond to the ECM states: if the communications device is inECM_connected, it should also be in RRC_connected and if it is inECM_idle, it should also be in RRC_idle. Discrepancies between ECM andRRC states may occur for a short period of time as a connection is beingset-up or torn-down. An illustration of the states of a communicationsdevice 101 which include both the ECM states and the RRC states isillustrated in FIG. 4.

As shown in FIG. 4 a communications device 101 may start in the RRCIdle/ECM Idle state when the device is off and not being used by theuser. The off state is therefore represented by a box 201. As soon asthe communications device 101 is activated it must connect to the MME105 in order to perform a tracking area update and to active services tothe communications device. Accordingly, the communications device movesinto an RRC connected state 204 but with the ECM Idle state because anEPS bearer has not yet been established. It is only after an EPS bearerhas been established that the communications device 101 moves into anRRC connected and ECM connected state 206. A general illustration of theprocess by which data is communicated via an EPS bearer after a UE movesfrom an off state to an ECM connected and RRC connected state this shownin FIG. 5.

FIG. 5 illustrates an example of the messages exchanged for setting up aconnection from the communications device 101 to the destination 120,for using the connection to communicate data and for releasing theconnection after the communications between the communications device101 and the destination 120 have been completed. The call flow of FIG. 5can be schematically divided into four steps A-D. Before step A starts,the communications device 101 is in the ECM_idle state which means thatthe communications device 101 is not currently communicating. At step A(messages 1-3) an RRC connection is set up between the communicationsdevice 101 and the eNB 102 for controlling communications between thecommunications device 101 and the eNB 102. Once this RRC connection hasbeen successfully established, at step B (messages 3-12), thecommunications device 101 can establish a NAS connection with the MME105. Following this NAS connection request from the communicationsdevice 101 to the MME 105, the MME sets up a connection (e.g. EPSbearer) between the communications device 101 and the P-GW 104, via theS-GW 103 and the eNB 102, and controls this connection. Although theyhave not been represented here, messages may also be sent to the P-GW104, for example from the S-GW 103, for setting up the connection (e.g.EPS bearer) at the P-GW 104, for example the GTP tunnel and EPS bearer.At the end of step B, the communications device 101 has an EPS bearerset-up and available to send and receive messages and is therefore inthe ECM-connected state. The call flow of FIG. 4 is an illustration andsome of the messages may vary, for example depending on the EMM statebefore step A. For example, the communications device may be inEMM_unregistered state and switch to EMM_registered during step B, ormay already be in EMM_registered before step A starts.

During step A, a RRC connection is setup between the communicationsdevice 101 and the eNB 102. Once this RRC connection has been set up, attime t₁, the eNB maintains an RRC context, referred to as Cont_RRC, forthe duration of the RRC connection. In other words, until the RRC isreleased, the eNB will maintain this Cont_RRC. Such a context may forexample include a communications device identifier (e.g. C-RNTI), powercontrol settings, mobility settings, security settings, other radiosettings or any other information. There will also be a correspondingcontext in the UE storing similar information pertaining to theoperation of the radio layers, however, this is not shown in thediagram.

Once the RRC connection has been set up, a NAS connection is set upbetween the communications device 101 and the MME 105. Once this NASconnection has been set up, at time t₂, the MME 105 maintains a contextfor this NAS connection to the communications device 101, referred to asCont_NAS, for the duration of the NAS connection. Such a NAS context mayfor example include a terminal identifier, a terminal's IP address, acurrent eNB, mobility settings, security settings, QoS settings, or anyother information. As explained above, when the communications device101 attaches/sets up a data connection via the mobile network, an EPSbearer is set up in the user plane between the communications device andthe P-GW 104, the bearer being controlled in the control plane by theMME 105. There will also be a context in the UE storing UE relatedinformation pertaining to the NAS protocol. Note that the contextCont_NAS shown in the diagram as being stored at the MME, may includemore information than just that used by or transferred in EPC NASsignalling procedures, it may also contain information pertaining to thesession which has been gathered by the MME from for example, an HSS.

Once the RRC connection, the NAS connection and the EPS bearer have beenset up, the communications device can send uplink data through the EPSbearer and to the destination. Even though in the example of FIG. 5, thecommunications device 101 sends uplink data, the same connection setupwould occur for a downlink or for an uplink and downlink transmission.Likewise the path of an acknowledgement message has been illustrated inthe example of FIG. 5 even though there may not be any acknowledgementmessage in other examples. As discussed earlier, this may for example bedependent upon the type of protocol(s) used for transmitting the data.

As can be seen in FIG. 5, Cont_RRC and Cont_NAS are maintained for theduration of the RRC and NAS connection (i.e. until they are expresslyreleased with a connection release message exchange) and, as a result,the RRC context is used for every packet that eNB 101 receives from orsends to the communications device 101. Once the EPS bearer can bereleased, the NAS connection between the communications device 101 andthe MME 105 is released at the same time. As a result, at the time t₃where the NAS connection is released, the context Cont_NAS is alsoreleased. The tearing down of the NAS connection is followed by atearing down of the corresponding RRC connection at time t₄. Again, asthe RRC connection is released, the context Cont_RRC is also released.

At a point in time after completion of step C, the resources arereleased (step D). Step D could happen at any time after step C, forexample just after message 20, or at a later point in time, for exampleafter the communications device 101 stopped communicating for apredetermined time. The aim of step D is to release all unusedconnections, that is, to release the NAS connection between the MME 105and the communications device 101 (also leading to the release ofresources such as the GTP tunnel between S-GW and eNB and the EPSbearer), and to release the RRC connection between the communicationsdevice 101 and the eNB 102. Again, depending on whether thecommunications device 101 should remain in EMM_registered after step Dor should switch to EMM_unregistered, the call flow for step D is likelyto be affected. For example, the communications device 101 may remain inEMM_registered if the communications device simply releases the RRCconnection, NAS connection and EPS bearer because it has been inactivefor too long, or the communications device 101 may de-attach from thenetwork and switch to EMM_unregistered (for example following a handoverto a GSM network).

Protocol Stack within Network Elements

As will be appreciated from those skilled in the art each of the networkelements shown in FIG. 5 performs various functions in order toestablish the EPS bearer and allow the communications device 101 to movefrom the EPM and RRC Idle states to the ECM connected and RRC connectedstates. This is achieved using various functions performed at each ofthe different protocol layers in both a user plane protocol stack and acontrol plane protocol stack. The functions performed by each of thenetwork elements are shown in FIG. 6. As shown in FIG. 6 the eNodeB 102includes and intercell radio resource management entity 301, a radiobearer controller 302, a connection management controller 304, a radioadmission control 306, an eNodeB measurement configuration and provisionentity 308 and a dynamic resource allocation or scheduler 310 whichoperate for example as explained in 3GPP document TS36.300 to provideradio resources to the communications communications device and tomanage the connection and mobility. In respect of the control planesignalling the MME communicates signalling messages to the eNodeB 102using an NAS security function 320, an Idle state mobility handling 322and an EPS bearer controller 304. Control plane functions or NASfunctions performed by the serving gateway include mobility anchoring330 as well as UPI address allocation performed by the P-GW 104 340 andpacket filtering 342.

Correspondingly the protocol stack for the control plane entitiesillustrated in FIG. 7 which facilitate the non access stratum (NAS)signalling is supported by a protocol stack which includes a relayresource connection layer 400, a packet data conversions protocol layer402, a radio link control layer 404, a medium access control layer 406and the physical layer 408.In contrast the user plane protocol stack is showing in FIG. 8 wherecorresponding elements showing in FIG. 7 are correspondingly labelled.

As will be appreciated by those skilled in the art, each of the layersin the protocol stack of the user plane and the control plane arerequired to monitor the current state of the transmission of data ateach of the protocol layers in order to maintain for example securityand data delivery to form the EPS bearer for communicating packet datafrom the communications device 101 across the mobile communicationsnetwork to the destination 120.

Stasis State

In the event that the communications device 101 has to send and/orreceive large amount of data, the connection method described above canbe efficient in setting up a high-throughput connection to the P-GW fortransmitting such data. It is however based on the exchange of a largenumber of signalling messages between different parties and the setup ofa large number of advanced connections (RRC, NAS, EPS, etc), which mayrender the system inefficient if the communications device'stransmission is actually a brief and small transmission, which is likelyto be the case for low complexity applications and more simple devicessuch as an MTC type applications. Such devices are likely to requirereduced functionality in comparison to conventional communicationsdevices, in order to reduce the cost of producing such devices. This isbecause it is envisaged that such devices will be more ubiquitous andutilitarian than conventional communications devices and thereforeshould be less expensive to produce in order to be attractive to usemobile communications networks to transmit and receive data. However thepresent disclosure is not limited to such devices and may findapplications operating with conventional devices in a different mode.Accordingly, the present technique aims to provide an advantage ofadapting conventional mobile communications techniques, particularly inrespect of data communications in order to reduce an overhead ofsignalling transmissions and processing with respect to useful datatransmitted and a cost of implementing communications devices which usethe techniques as provided by an adapted mobile communications network.This is because recent networks, including LTE networks, have beendesigned for high-capabilities and high-mobility communications devicesand, as a result, they usually provide for the setup of a high-speedhigh-reliability connection with an advanced mobility management with aview to supporting communications devices potentially transmitting largeamount of data while moving. However, in the case of a communicationsdevice that is not moving as much as a personal phone and/or transmitsonly small amount of data on a relatively infrequent basis, the amountof signalling and of mobility tracking required for the communicationsdevice to communicate may be excessive. In particular, it may beexcessive compared to the sometimes low level of service that may beacceptable for this type of communications devices. For example MTCcommunications devices are more delay-tolerant than a human-to-humancommunications device, are less likely to move and/or to change cellduring transmissions and usually send or receive small amount of data.

It may therefore be desirable to provide ways to improve an efficiencyof the network for transmitting small messages and/or MTCcommunications. One example is disclosed in our co-pending UK patentapplications numbers 1113145.5, 1113144.8, 1209526.1 and Internationalpatent application number PCT/GB2012/051764 the contents of which areincorporated herein by reference.

According to the present technique embodiments of the present disclosureare arranged such that a mobile communications device which no longerhas data to send for a predetermined time enters a stasis states bytransmitting a signal to the mobile communications network and moreparticularly in the present example to an eNodeB 102. Once the eNodeB102 receives the stasis message then in order to avoid having to performall of the signalling required to set up an EPS bearer again, thecurrent state of each of the protocol stacks for the current EPS bearerare saved by the eNodeB and other network elements. Accordingly, forexample the communications device 101 retains the connection identifierwhich is used by the network to support the RRC connection and ECMconnection state such as for example the CRNTI.

Embodiments of the present technique will be illustrated with referenceto a more detailed call flow diagram corresponding to the exampleshowing in FIG. 5. FIGS. 9a and 9b illustrate signalling transitions andmessages which are required for the communications device 101 to passfrom an RRC Idle and ECM Idle state to an RRC connected and ECMconnected state back to the ECM Idle and RRC Idle state. In FIG. 9a froma start state, in which the communications device 101 is in the RRC Idleand ECM Idle state 201, the communications device 101 performs a randomaccess procedure 501 in order to request and be granted uplink resourcesin order to transmit an RRC connection request message 502. The eNode-B102 responds with a RRC connection set up message 504 and an RRCconnection set up complete message. At this point the communicationsdevice 101 is in the RRC connected but ECM Idle state. Following the RRCconnection set up complete message, the communications device 101transmits an attach request/PDM connection request to the eNode-B 102506. The eNode-B 102 then forwards the attached request/PDN connectivitymessage 508 to the MME 105 in order to establish an EPS bearer.Following transmission of the attached request/PDM connectivity request508 the MME 105 and the eNodeB 102 and the communications device 105,102, 101 perform a security procedure 510 in order to authenticate thecommunications device. After this process a context is established forthe communications device for the EPS bearer. Accordingly, the MME 105transmits an initial context set up request/attach accept, activatedefault bearer context request 512 to the eNodeB 102 which then forwardsan RRC connection reconfiguration or attach accept/active default bearermessage 514. The communications device 101 then transmits an RRCconnection reconfiguration complete message 514 and in response theeNodeB 102 transmits and initial context set up response message 516 tothe MME 105. The eNodeB 102 transmits an RLC Ack message 518 to thecommunications terminal 101. The communications device 101 thentransmits an uplink information transfer attach complete/active acceptmessage 518 which prompts the eNodeB 102 to transmit an uplink NAStransport (attach complete/active default accept message 520). Afterthis message the eNodeB 102 transmits an RLC Ack message 522 at whichpoint the communications device moves to the RRC connected/ECM connectedstate 206.

FIG. 9b shows the message flow for moving from the RRC connected and ECMconnected states to the RRC Idle and ECM Idle states corresponding thecall flow diagram showing in FIG. 9a . As shown in FIG. 9b thecommunications device 101 is transmitting uplink data using transmissionmessages 530 which are acknowledged by the eNodeB 102 with a downlinkdata message 532 providing an RLC Ack. The data transmitted on theuplink to the eNodeB 102 is then forwarded to the PGN 104 via theestablished EPS bearer 534. It then follows a TCP Ack transmitted on thedownlink and messages associated with a transmission of acknowledgementof downlink data transmissions 536. After the communications terminal101 has transmitted an uplink data RLC acknowledgement message 540 whichcould be the final data transmission for the uplink by thecommunications device 101, the communications device 101 may determinethat there is no more data to send as represented by the box X 542. Onlythe eNodeB (communication device 102) can release the RRC connection,provided for the communications device 102, using an RRC connectionrelease message by detecting a period of inactivity. Releasing the RRCconnection will normally be the context at the eNodeB and MME (howeverthis is dependent on network implementation). This release follows andexchange of messages 544 to release the RRC connect and also release thecommunications context of the communications terminal 101 using messagesexchanged between the eNodeB and the PGW 104.

FIG. 10 provides an example of the present technique in which thecommunications device 101 includes a new stasis state for the RRC state.Thus as shown in FIG. 10 which corresponds to FIG. 4, a new stasis state250 is provided to an adapted communications device 101. As explainedabove in the new stasis state the state of the protocols within theprotocol stack on both the eNode-B 102 and the UE 101 are effectivelyfrozen and stored and the C-RNTI for the UE is saved by the eNodeBpending further communications. However, the radio resources arereleased.

A state diagram showing the changes of the state by the communicationsdevice to reach the stasis state 250 is shown in FIG. 11, where thestates are numbered in correspondence with those of FIGS. 4 and 10. Themessage state flow is summarised with respect to the numbering of thestate transitions shown in FIG. 11 as follows:

-   -   1. A communications device determines that either it has no more        data to transmit on the uplink to the communications network or        that it does not expect to receive any further data on the        downlink. In the former case the communications device will        monitor the data buffer containing packet for transition on the        uplink. In the latter case if the communications device detects        that there are no more data packets to send to the        communications device 101 then this may be signalled to the        communications 101. The point at which the communications device        therefore decides that it has no more requirements for        communications resources is identified with the point “x” in        FIG. 9b . In order to enter the RRC stasis state 250, the        communications device 101, whilst in the RRC connected and ECM        connected state 206, transmits an RRC stasis request message in        state 206 before it can transition to the RRC stasis and ECM        connected state 250.    -   2a. The communications device then receives and RRC stasis        confirm message and moves from the RRC connected/ECM connected        state 206 to the RRC stasis and ECM connected state 250.    -   2b. In some circumstances the communications device 101 may        receive an RRC stasis reject message from the communications        network, for example where the communications network finds that        it now has data to send to the communications device or if the        stasis mode for both the eNode-B and the communications device        is not supported by the mobile communications network.    -   3. The communications device then decides that it should        transmit data for example, as a result of new data being ready        to be transmitted in the device's packet data buffer. Thus        having received a packet for transmission the communications        device needs to move back to the RRC connected and ECM connected        state 206. Another reason for moving back to the RRC connected        and ECM connected state 206 is that measurements performed by        the communications device might indicate that it should hand        over to another eNode-B in which case a communications device        must be in the RRC and ECM connected state 206.    -   4. The communications device initiates the RACH procedure for        example the MAC layer transmission described in section 5.1.5 of        TS36.321. This essentially involves transmitting random access        message using contention access as it conventionally arranged        with mobile communications network. The PRACH includes the CRNTI        which was previously stored by the communications device and by        the eNodeB 102. As such when the eNodeB receives the CRNTI of        the communications device in the PRACH message the eNodeB can        immediately recognise that the communications device transmitted        the PRACH message and also recognised that the communications        device 102 concerned is currently in the stasis state 250. The        eNodeB therefore moves the communications device back to the RRC        connected ECM connected state 206 and transmits an RRC        connection re-establishment request message to the        communications device 101.    -   5. Therefore on completion of the RACH procedure (RAR received)        communications device transmits the RRC connection        re-establishment request message to the eNodeB 102. On receipt        of the RRC connection of establishment message the        communications device has then successfully re-established the        RRC connection and moves to the RRC connected/ECM connected        state 206.    -   6. If the communications device receives an RRC connection        re-establishment reject message then a communications device        transitions back to the RRC Idle but ECM connected state 252.

A call flow diagram corresponding to the core flow diagrams shown inFIGS. 9a and 9b but adapted in accordance with the present technique toinclude the call flow messages associated with a transition to thestasis state 250 is shown in FIG. 12. FIG. 12 is now summarised asfollows:

Starting from the RRC connected/ECM connected state 206 thecommunications device 101 transmits data packets on the uplink andreceives acknowledgment on the downlink or receives downlink datapackets and transmits acknowledgements on the uplink as explained withreference to FIGS. 5, 9 a and 9 b. This effective therefore forms partof section C of the flow diagram of FIG. 5. At point X in FIG. 12 thecommunications device 101 detects that it has no more data packets totransmit and transmits an RRC stasis message request 600. If thecommunications network can support the new stasis state then thecommunications network transmits an RRC stasis message confirm messageto the communications device 101 as message 602. At this point both thecommunications device and the eNode-B confirm that the CRNTI the RLC andPDCP sequence numbers and the MAC configuration etc. are to be retainedand stored so that effectively the EPC bearer moves into a stasis statein that it still exists but there are no packets being transmitted viathe EPS bearer.

Accordingly, when the communications terminal transmits data packetsagain via the EPS bearer there is no need to re-establish the tunnellingbetween the various nodes of the communications network in order toestablish the EPS bearer. The communications device 101 then transmits aRRC stasis ECM connected message 604 to the eNodeB to confirm that ithas entered the stasis state. Therefore in a period E the communicationsdevice has entered the stasis state 250.

Whilst in the stasis state 250 the communications device detects that itneeds to move back to the RRC connected and ECM connected state 206.This can be to transmit data from the uplink because the communicationsdevice detects that it has new packet data to be transmitted.Alternatively the network may detect that it may need to transmit on thedownlink and therefore signals to the communications device using aconventional paging message that it needs to move back to the RRCconnect and ECM connected states. Alternatively, the communicationsterminal which continues to monitor neighbouring base stations and maydecide that it needs to hand over to one of the neighbouring basestations as a result of measurement of radio link quality being taken inaccordance with a conventional handover arrangement.

Again, this would require the communications device 101 to move back tothe RRC connected/ECM connected state 206. In order for thecommunications device 101 to move back to the ECM connected/RRCconnected state 206, the communications device transits a PRACH message.The communications device receives but then discards the C-RNTI assignedvia the RAR message 608 and uses the retained C-RNTI. The C-RNTI whichwas retained should not be used by any other communications device.Accordingly the eNodeB 102 reserves the C-RNTI for the communicationsdevice during a time when the communications device is in the stasisstate so that this is not allocated to another communications device inthe cell. The RRC connection request re-establishment request message610 sent by the communications terminal 101 includes the retainedC-RNTI. The RRC connection re-establishment request message may includean indication of a status of the packet communications buffer stasis.The eNode-B 102 then transmits and RRC connection re-establishmentmessage 612 to the communications device 101 which responds with an RRCconnection re-establishment complete message 614. At this point thecommunications device has returned to the RRC connected/ECM connectedstate 206 and transmits data on the uplink in accordance with aconventional operation identified as a phase C shown in FIG. 5 and alsoin the first part of FIG. 12.

As will be appreciated by transitioning to the stasis state thecommunications terminal can release its radio communications resourcesand enter a power down state thus saving power. However, if there is newdata to be transmitted communications device does not have to proceedthrough the entire message exchange shown in FIGS. 9a and 9b in order tocommunicate packet data again. This is because the stats of the protocolstacks are retained for example the RLC layer and PDCP sequence numbersare maintained as well as the MAC configuration for the communicationslink. In addition on the network side the EPS bearer is also retainedand just needs to be reactivated by transmitting data packets in aconventional arrangement. Accordingly, it is possible to reduce networkresources consumed the result of signalling and reduce an amount ofredundant information which is communicated in order to establish theEPS bearer.

A diagram of an adapted communications device 101 and eNodeB 102 whichprovides an example embodiment of the present technique is shown in FIG.13.

As shown in FIG. 13, a communications device also referred to as a UE101 comprises a transmitter and receiver unit 701 and a controller 702.The controller 702 controls the transceiver unit 701 in order totransmit and receive data which is fed to a processor 704 which hostsapplications programs and other processes for providing user servicesand for controlling the communications device 101. Data transmitted onthe down-link and received for transmission on the up-link by thecommunications device 101 is fed to a data buffer 706. The data buffer706 buffers the data packets for transmission on the uplink to themobile communications network or buffers data packets received on thedownlink which are transmitted from and the eNodeB 102 to thecommunications device 101. As explained above when the communicationsdevice enters the stasis state, the state of the protocol stacksincluding sequence numbers, security keys etc are stored in a data store708 with a channel identifier such as a C-RNTI. This information, whichis related to the communications context of the communications devicecan be used to reactivate the communications context of thecommunications device 101 which has been used to transmit data packetson the uplink or receive data packets on the downlink via the EPS beareracross the mobile communications network, which is associated with thecommunications context.

Also shown in FIG. 13 is a base station or eNodeB 102, which comprises atransmitter and receiver unit 720 and a controller at 722. An adaptedschedulers 724 is used to schedule the allocation of uplink and downlinkcommunications resources in accordance with a conventional operation.However in combination with controller 722, when a stasis state messageis received from a communications device 701, the controller 722arranges for the corresponding state of the protocol stack associatedwith the EPS bearer establish for the communications device to be storedin a data store 726. The communications buffer 728 is provided to bufferdata packets received from respective EPS bearers for transmission tocommunications devices within a cell served by the eNodeB 182.Therefore, as explained above, once a stasis state message is detectedby the controller 722, a scheduler 724 releases communications resourcesallocated to communications terminal 101 which has entered the stasisstate and the controller 722 stores the state of the protocol stackincluding sequence numbers and security keys. The controller 722 thenarranges to transmit a message to the communications channel 101indicating a time for which the communications Tamil will remain withinthe stasis state.

Summary Aspects of the Stasis State

Embodiments of the present technique can provide new RRC state and theprovision of an efficient signalling procedure for the rapid transitionbetween the new state and RRC_CONNECTED. The new state differs fromexisting LTE RRC states (see TS 36.300 Section 7.2) in that

-   -   the RRC context is suspended (i.e. it is dormant) until        reactivated by the UE        -   the UE is not contactable        -   the RRC context is reactivated via the RACH procedure and            re-establishment of the RRC connection    -   network controlled handover is only possible as a result of UE        triggered activity related to measurements performed in the new        state

The UE must reactivate its RRC context (via the RACH procedure andre-establishment of the RRC connection, to change the state toRRC_CONNECTED) in order to transmit data. A UE may deactivate its RRCcontext via RRC signalling when RRC_CONNECTED. In this new stasis state:

-   -   The communication context in the UE and E-UTRAN is maintained;        -   the C_RNTI is maintained        -   the UE remains PMM_CONNECTED        -   RLC and PDCP Sequence Numbers are preserved        -   The MAC configuration is preserved        -   the security context is maintained (security keys/sequence            numbers are preserved in order to enable ciphering an            integrity protection)    -   E-UTRAN knows the cell which the UE belongs to;    -   Network ability to transmit and/or receive data to/from the UE        is suspended;    -   the UE's ability to transmit and/or receive data to/from network        is suspended    -   Any dedicated radio resources previously assigned to the UE        (e.g. PUCCH) are released    -   The UE performs neighbour cell intra-frequency measurements        according to the intra frequency neighbour list previously        provided (excluding blacklisted cells)        -   Event Reporting is triggered (Event A5) if S_(rxlev) falls            below quality threshold 1 and a neighbour cell is found            which is better than threshold2    -   UE triggers signalling to initiate transition to RRC_CONNECTED        when it has data to send or needs to provide a measurement        report or expects to receive data (according to information        provided by higher layers)    -   The Network (i.e. eNB) may buffer any DL data and/or NAS        messages and may attempt to deliver on transition to        RRC-CONNECTED    -   Network controlled mobility (handover), the network's ability to        transmit and/or receive data to/from the UE and the UE's ability        to transmit and/or receive data to/from the network is restored        on transition to RRC_CONNECTED.    -   In RRC_CONNECTED/PMM_CONNECTED the UE may send stasis state        message when it has no data to send and does not expect to        receive any data (X in FIG. 12). In RRC_CONNECTED/PMM_CONNECTED,        receipt of stasis state message causes the eNodeB to preserve        the UE's current communications context and to maintain the UE's        packet tunnel between the eNB and Packet Gateway.    -   The MAC configuration, PDCP and RLC states, including sequence        numbers and security context (sequence numbers and keys related        to ciphering an integrity protection) are then maintained by the        eNodeB and UE.    -   In RRC_CONNECTED/PMM_CONNECTED, the eNodeB may respond to        receipt of stasis state message by sending stasis state eject        message to the UE if it does not wish to preserve the UE's        current RRC context (as identified by the C-RNTI).    -   The eNodeB may send a RRC stasis state confirm message in        response to the received stasis state message in order to        indicate that the UE's RRC context is suspended/dormant and        RRCNewMessageXConfirm will include an Information Element        providing timer value T_(NewState), where T_(NewState)        indicating the period of time for which the communication        context is maintained. The value of T_(NewState) may be        configured by the network operator and is would have a value of        several hours. While T_(NewState)≠0, the communication context        is maintained; the eNB does not rassign the C-RNTI to any other        UE and preserves current RLC and PDCP sequence numbers, MAC        configuration and security related information and packet tunnel        between the eNB and Packet Gateway). Whenever T_(NewState)≤0        then the eNB may end the communications context (i.e. it may        delete it from its memory). If the communication context is        ended then the eNB no longer has any knowledge relating to the        UE and may reassign the C-RNTI.    -   If stasis state confirm message is received in response to        stasis state message sent then the UE enters RRC-stasis state        (step E area of FIG. 12). The UE is moved to RRC_stasis state        only when it receives RRC stasis state confirm message. If it        receives a RRC stasis state reject message or if it does not        receive any response to the stasis state message then it remains        in the state RRC_CONNECTED.    -   The support of the RRC stasis state is assumed to be optional in        the UE and in the network. If the eNodeB does not support        RRC_stasis state then the eNodeB will ignore/discard the RRC        stasis state message request and will not respond to it. If the        eNodeB is unable to maintain the communications context (e.g.        due to processing or memory limitations) then it should send RRC        stasis state Reject message in response to a received RRC stasis        state Request.    -   In RRC_stasis state, the UE continues to monitor its current        cell and it may continue to use the intra frequency neighbor        list and cell blacklist, provided in RRC_CONNECTED.    -   If S_(rxlev) (current cell)<threshold1 then the UE attempts to        find a cell in its neighbour list which is not in its blacklist        and for which S_(rxlev) (new cell)>threshold2 (threshold1 and        threshold2 are assumed to be operator defined and may be stored        in the USIM). If these conditions are met then this triggers        sending of an Even Report (Event A5) to the eNodeB.    -   If T_(NewState) expires then the UE moves to RRC_IDLE.    -   If the UE has data in its output buffer (buffer status report,        application layer data, triggered event report etc.) then it        follows the Random Access Procedure specified for LTE (see        section 5.1 of 36.321) in order to obtain a Timing Advance and        an UL Grant. The UE discards the C-RNTI provided by the Random        Access Response (see Section 5.1.5 of 36.321) and then proceeds        to re-establish the RRC connection (according to Section 5.3.7.4        of TS 36.331).

In some examples applications in terminal devices (laptops etc.)initiate communication session establishment with servers and servers donot generally initiate session establishment with terminal devices.Embodiments can therefore provide a means of improving utilisation ofthe use of radio resources in the case where the mobile device (the UE)initiates session establishment with some remote server and hasinformation governing sending/receiving of data to/from the server. Thedisclosure provides a means to enable a UE which occasionally wishes totransmit to or receive small amounts of data to maximise sleep mode(i.e. to shut down most of its radio processes). Radio processes areswitched off when the UE has no data to send and does not expect toreceive any data.

In RRC_NewState most radio processes are switched off while the UEstransmit buffer is empty then

-   -   the UE monitors only its current cell    -   if the received signal level S_(rxlev) falls below threshold1        then        -   it tries to find a neighbour cell which is not an the            blacklist and which has a signal level above threshold2        -   if suitable is found then this triggers sending an Event            Report (so Event Report A5 is placed in the UE's transmit            buffer)            If the UEs transmit buffer is not empty for a certain time            or contains more than a certain number of bytes then radio            processes are switched back on and the UE performs the RACH            procedure (according to Section 5.1 of 36.321) and obtains a            Timing Advance to resynchronize with the eNB and an UL Grant            in order to commence transmission of buffered data (the UE            continues to reuse the C-TNTI previously assigned, before            transition to RRC_stasis state—according to Section 5.1.5 of            36.321)            The disclosure has been described with reference to LTE, but            may also be applicable in other wireless communication            systems, such as UMTS, as well as in both FDD and TDD            systems. The disclosure can be applied regardless of whether            or not DRX functionality is supported, and DRX functionality            provides opportunities to optimise sleep during periods of            data transmission/reception but is not optimal during long            period of inactivity (e.g. several minutes).            Advantages provided by the present technique may depend on            the frequency of the occasional data transmissions (e.g.            every minute, every 5 minutes) and amount of data to be            transmitted. For example: Greater power saving might be            achieved if the UE waited until some threshold is            reached—buffer is not empty for a certain time and/or            reaches a certain occupancy (numbers of bytes stored).

The disclosure can find application MTC devices, e.g. smart metering,where the UE is stationary and may want to send small amounts of data(e.g. 100 bytes) every few minutes, every few hours, once per day.

Various further aspects and features of the present invention aredefined in the appended claims. As will be appreciated although theexample of an LTE communications system has been used to illustrateexamples of the present technique, the present disclosure fined equalapplication with other communications systems. Thus although the stateECM connected and EMM connected have been used, other communicationssystems use the term PMM connected to represent a packet mobilitymanagement system which corresponds substantially to the ECM/EMMterminology used in the present disclosure.

Various further aspects and features of the present disclosure aredefined in the appended claims. Various combinations of the features ofthe dependent claims may be made with those of the independent claimsother than the specific combinations recited for the claim dependency.Embodiments of the present disclosure have been defined largely in termsof reduced capability devices transmitting data via a virtual carrierinserted in a conventional LTE based host carrier. However, it will beunderstood that any suitable device can transmit and receive data forexample devices which have the same capability as a conventional LTEtype device or devices which have enhanced capabilities.

Various further aspects and features are defined in the followingnumbered clauses:

1. An infrastructure equipment for forming part of a mobilecommunications network, the infrastructure equipment comprising:

a transmitter unit configured to transmit data to communications devicesvia a wireless access interface,

a receiver unit configured to receive data transmitted fromcommunications devices via the wireless access interface, and

a controller configured to control the transmitter unit and the receiverunit to form the wireless access interface,

to receive one or more signalling messages from a communications deviceand in response to establish a communications context for communicatingdata packets via a packet communications bearer via the mobilecommunications network,

to receive a stasis state message from the communications device forwhich the context has been established, the stasis state messageindicating that the communications device wishes to enter a stasis statebecause no data packets are available for transmission for apredetermined time via the packet communications bearer,

to transmit a stasis state confirm message to the communications device,and

to store information relating to the communications context establishedfor the communications devices and associated with the packetcommunications bearer in a data store, which stored information can beused by the controller to re-establish the same packet communicationsbearer to transmit data packets via the same packet communicationsbearer, the communications device thereby entering the stasis state.

2. An infrastructure equipment according to clause 1, wherein thecontroller is configured in response to the stasis state message tostore, with the information relating to the communications context, anetwork terminal identifier provided to the communications device forrequesting communications resources when the communications context wasestablished, receiving a request to re-connect message from thecommunications device, the request to re-connect message including thenetwork terminal identifier,

in response to receiving the request to re-connect message from thecommunications device the controller is configured

to recognise the network terminal identifier,

to retrieve the information relating to the communications context ofthe communications device from the data store,

to re-establish the communications context of the communications device,to communicate data packets received from the communications device viathe wireless access interface and the mobile communications network viathe packet communications bearer.

3. An infrastructure equipment according to clause 1 or 2, wherein theinformation relating to the communications context which is stored bythe controller in the data store includes one or more sequence numbersassociated with one or more protocols of a protocol stack which formsthe packet communications bearer to the effect that, when thecommunications device moves from the stasis state to the connectedstate, the stored sequence numbers can be restored to the one or moreprotocols of the protocol stack to transmit or receive data packets viathe wireless access interface and the packet communications bearer.

4. An infrastructure equipment according to clause 3, wherein theinformation relating to the context which is stored by the controller inthe data store includes one or more of a sequence number associated witha radio link control protocol, a packet data communications protocol ora configuration of a medium access control layer.

5. An infrastructure equipment according to clause 3 or 4, wherein theinformation relating to the context which is stored by the controller inthe data store includes a sequence number and a cyphering key associatedwith a sequence context.

6. An infrastructure equipment as claimed in any of Claims 1 to 5,wherein the infrastructure equipment is configured to operate inaccordance with a 3GPP Long Term Evolution network, the terminalidentification number of the communications device being an Cell-RadioNetwork Terminal Identifier, C-RNTI, and the packet communicationsbearer is an Enhanced Packet System communications bearer.

7. A mobile communications network including an infrastructure equipmentas claimed in any of claims 1 to 6.

8. A method of communicating data packets from an infrastructureequipment via a mobile communications network, the method comprising:

receiving one or more signalling messages from a communications device,

in response to the received signalling messages establishing acommunications context for communicating data packets using a packetcommunications bearer via the mobile communications network,

receiving a stasis state message from the communications device forwhich the context has been established, the stasis state messageindicating that the communications device wishes to enter a stasis statebecause no data packets are available for transmission for apredetermined time via the packet communications bearer,

transmitting a stasis state confirm message to the communicationsdevice, and

storing information relating to the communications context establishedfor the communications devices and associated with the packetcommunications bearer in a data store, which stored information can beused by the controller to re-establish the packet communications bearerto transmit data packets using the packet communications bearer, thecommunications device thereby entering the stasis state.

9. A method according to clause 8, wherein the storing informationrelating to the communications context established for thecommunications devices comprises

in response to the stasis state message storing, with the informationrelating to the communications context, a network terminal identifierprovided to the communications device for requesting communicationsresources when the communications context was established,

receiving a request to re-connect message from the communicationsdevice, the request to re-connect message including the network terminalidentifier, and

in response to receiving the request to re-connect message from thecommunications device,

recognising the network terminal identifier,

retrieving the information relating to the communications context of thecommunications device from the data store, and

re-establishing the communications context of the communications device,to communicate data packets received from the communications device viathe wireless access interface and the mobile communications network viathe packet communications bearer.

10. A method according to clause 8 or 9, wherein the storing informationrelating to the communications context established for thecommunications devices and associated with the packet communicationsbearer in a data store comprises

storing in the data store one or more sequence numbers associated withone or more protocols of a protocol stack which forms the packetcommunications bearer to the effect that, when the communications devicemoves from the stasis state to the connected state, the stored sequencenumbers can be restored to the one or more protocols of the protocolstack to transmit or receive data packets via the wireless accessinterface and the packet communications bearer.

11. A mobile communications system comprising a mobile communicationsnetwork according to clause 7 providing a wireless access interface forcommunicating with the communications device, and a communicationsdevice for transmitting data to and receiving data from the mobilecommunications network, the communications device comprising:

a transmitter unit configured to transmit signals to the mobilecommunications network via the wireless access interface provided by themobile communications network, and

a receiver unit configured to receive signals from the mobilecommunications network via the wireless access interface provided by themobile communications network, and

a controller configured to control the transmitter unit to transmit oneor more signalling messages to the communications network and thereceiver unit to receive one or more signalling messages from thecommunications network to establish a communications context forcommunicating data packets using a packet communications bearer from thecommunications device via the mobile communications network, wherein thecontroller is configured

to identify that the communications device can enter a stasis statebecause no data packets are available for transmission for apredetermined time via the packet communications bearer or there are nodata packets to receive via the packet communications bearer,

to transmit a stasis state message to the mobile communications network,and

to store information relating to the communications context associatedwith the packet communications bearer in a data store, which storedinformation can be used by the controller using the transmitter unit andthe receiver unit to re-establish the packet communications bearer totransmit and/or receive data packets using the packet communicationsbearer, the communications device thereby entering the stasis state.

What is claimed is:
 1. An infrastructure equipment for forming part of amobile communications network, the infrastructure equipment comprising:a transmitter configured to transmit data to communications devices viaa wireless access interface; a receiver configured to receive datatransmitted from the communications devices via the wireless accessinterface; and a controller configured to: control the transmitter andthe receiver to form the wireless access interface, receive one or moresignaling messages from a communications device and, in response,establish a communications context for communicating data packets via apacket communications bearer via the mobile communications network,receive a stasis state message from the communications device for whichthe context has been established, the stasis state message indicatingthat the communications device wishes to enter a stasis state because nodata packets are available for transmission for a predetermined time viathe packet communications bearer, wherein during the stasis state,information relating to the communications context associated with thepacket communications barrier is stored, radio resources associated withthe communications context are configured to be released, and thecommunications device is configured to enter a power down state,transmit a stasis state confirm message to the communications device,and store information relating to the communications context establishedfor the communications devices and associated with the packetcommunications bearer in a data store, wherein the stored information isconfigured to be used by the controller to re-establish the same packetcommunications bearer to transmit data packets via the same packetcommunications bearer, the communications device thereby entering thestasis state, wherein, when the communications device is in the stasisstate, the controller is further configured, in combination with thereceiver, to: transmit a connection re-establishment message to thecommunications device, receive a connection re-establishment completemessage from the communications device in accordance with measurementsat the communications device having satisfied predetermined conditions,and re-establish the same packet communications bearer in the cell. 2.The infrastructure equipment of claim 1, wherein the controller isconfigured in response to the stasis state message to: store, with theinformation relating to the communications context, a network terminalidentifier provided to the communications device for requestingcommunications resources when the communications context wasestablished; receive a request to re-connect message from thecommunications device, the request to re-connect message including thenetwork terminal identifier; recognise the network terminal identifierin response to receiving the request to re-connect message from thecommunications device; retrieve the information relating to thecommunications context of the communications device from the data store;re-establish the communications context of the communications device;and communicate data packets received from the communications device viathe wireless access interface and the mobile communications network viathe packet communications bearer.
 3. The infrastructure equipment ofclaim 1, wherein the information relating to the communications contextwhich is stored by the controller in the data store includes one or moresequence numbers associated with one or more protocols of a protocolstack which forms the packet communications bearer to the effect that,when the communications device moves from the stasis state to theconnected state, the stored sequence numbers can be restored to the oneor more protocols of the protocol stack to transmit or receive datapackets via the wireless access interface and the packet communicationsbearer.
 4. The infrastructure equipment of claim 3, wherein theinformation relating to the context which is stored by the controller inthe data store includes one or more of a sequence number associated witha radio link control protocol, a packet data communications protocol ora configuration of a medium access control layer.
 5. The infrastructureequipment of claim 3, wherein the information relating to the contextwhich is stored by the controller in the data store includes a sequencenumber and a cyphering key associated with a sequence context.
 6. Theinfrastructure equipment of claim 1, wherein the infrastructureequipment is configured to operate in accordance with a 3GPP Long TermEvolution network, the terminal identification number of thecommunications device being an Cell-Radio Network Terminal Identifier,C-RNTI, and the packet communications bearer is an Enhanced PacketSystem communications bearer.
 7. A mobile communications networkincluding the infrastructure equipment of claim
 1. 8. A mobilecommunications system comprising a mobile communications network ofclaim 7 providing a wireless access interface for communicating with thecommunications device, and a communications device for transmitting datato and receiving data from the mobile communications network, thecommunications device comprising: a transmitter configured to transmitsignals to the mobile communications network via the wireless accessinterface provided by the mobile communications network, a receiverconfigured to receive signals from the mobile communications network viathe wireless access interface provided by the mobile communicationsnetwork; and a controller configured to: control the transmitter totransmit one or more signaling messages to the communications networkand the receiver to receive one or more signaling messages from thecommunications network to establish a communications context forcommunicating data packets using a packet communications bearer from thecommunications device via the mobile communications network, identifythat the communications device can enter a stasis state because no datapackets are available for transmission for a predetermined time via thepacket communications bearer or there are no data packets to receive viathe packet communications bearer, wherein during the stasis state,information relating to the communications context associated with thepacket communications barrier is stored, radio resources associated withthe communications context are configured to be released, and thecommunications device is configured to enter a power down state,transmit a stasis state message to the mobile communications network,and store information relating to the communications context associatedwith the packet communications bearer in a data store, which storedinformation can be used by the controller using the transmitter and thereceiver to re-establish the packet communications bearer to transmitand/or receive data packets using the packet communications bearer,release the radio resources relating to the communications context, andcontrol the communications device to enter the power down state, thecommunications device thereby entering the stasis state, wherein when inthe stasis state, the controller is configured in combination with thereceiver to: monitor signals received via the wireless access interface,perform measurements on the monitored signals, and re-establish the samepacket communications bearer in the cell in accordance withpredetermined conditions based on the measurements.
 9. A method ofcommunicating data packets from an infrastructure equipment via a mobilecommunications network, the method comprising: receiving one or moresignaling messages from a communications device, in response to thereceived signaling messages, establishing a communications context forcommunicating data packets using a packet communications bearer via themobile communications network; receiving a stasis state message from thecommunications device for which the context has been established, thestasis state message indicating that the communications device wishes toenter a stasis state because no data packets are available fortransmission for a predetermined time via the packet communicationsbearer, wherein during the stasis state, information relating to thecommunications context associated with the packet communications barrieris stored, radio resources associated with the communications contextare configured to be released, and the communications device isconfigured to enter a power down state, transmitting a stasis stateconfirm message to the communications device; and storing informationrelating to the communications context established for thecommunications devices and associated with the packet communicationsbearer in a data store, wherein the stored information is configured tobe used by the controller to re-establish the packet communicationsbearer to transmit data packets using the packet communications bearer,the communications device thereby entering the stasis state, wherein,when the communications device is in the stasis state, the methodfurther comprises: transmitting a connection re-establishment message tothe communications device, receiving a connection re-establishmentcomplete message from the communications device in accordance withmeasurements at the communications device having satisfied predeterminedconditions, and re-establishing the same packet communications bearer inthe cell.
 10. The method of claim 9, wherein storing informationrelating to the communications context established for thecommunications devices comprises: in response to the stasis statemessage storing, with the information relating to the communicationscontext, a network terminal identifier provided to the communicationsdevice for requesting communications resources when the communicationscontext was established; receiving a request to re-connect message fromthe communications device, the request to re-connect message includingthe network terminal identifier; recognizing the network terminalidentifier in response to receiving the request to re-connect messagefrom the communications device; retrieving the information relating tothe communications context of the communications device from the datastore; and re-establishing the communications context of thecommunications device to communicate data packets received from thecommunications device via the wireless access interface and the mobilecommunications network via the packet communications bearer.
 11. Themethod of claim 9, wherein storing information relating to thecommunications context established for the communications devices andassociated with the packet communications bearer in a data storecomprises: storing in the data store one or more sequence numbersassociated with one or more protocols of a protocol stack which formsthe packet communications bearer to the effect that, when thecommunications device moves from the stasis state to the connectedstate, the stored sequence numbers can be restored to the one or moreprotocols of the protocol stack to transmit or receive data packets viathe wireless access interface and the packet communications bearer.